Physiological means for altering the lipid fluidity of cell membranes are screened. Analysis of the ensuing effect on cellular function has indicated a direct relation to the induced change in the degree of exposure and diffusion rates of the relevant membrane proteins. Our attention is now mostly focused on the effect of lipid fluidity on the degree of exposure of receptors in brain membranes and antigens in tumor cells. Methods for hyper-rigidification of cell membranes which may lead to shedding of these components are being sought. Tumor immunization with lipid-treated syngeneic tissues is studied in detail in an attempt to devise a new non-poisonous tool for immunotherapy of cancer. The possibility, that over-exposed membrane constituent can evoke an autoimmune response, is planned to be studied.